Check Power Supply And Ground Line Of Engine Control Module (ECM): Wiring Diagram

Engine Electrical System ENGINE TYPE FB (WITHOUT PUSH BUTTON START) <Ref. to ENGINE PERFORMANCE (Legacy), ENGINE PERFORMANCE (Outback), Engine Electrical System.>
Engine Electrical System ENGINE TYPE FB (WITH PUSH BUTTON START) <Ref. to ENGINE PERFORMANCE (Legacy), ENGINE PERFORMANCE (Outback), Engine Electrical System.>

Fig 1: Engine Control Module (ECM) Power Supply And Ground Line - Wiring Diagram
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTICS PROCEDURE

Step	Check	Yes	No
1 CHECK M/B (MAIN RELAY) . Turn the ignition switch to OFF. Remove the M/B (main relay). Connect the battery to M/B (main relay) terminals No. 2 and No. 4. Measure the resistance between M/B (main relay) terminals. Terminals No. 1 - No. 3:	Is the resistance less than 1 Ω?	Go to step 2 .	Replace the M/B (main relay). <Ref. to MAIN RELAY .>
2 CHECK GROUND CIRCUIT FOR ECM . Disconnect the connector from ECM. Measure the resistance of harness between ECM connector and chassis ground. Connector & terminal (E158) No. 61 - Chassis ground: (E158) No. 62 - Chassis ground: (E158) No. 63 - Chassis ground: (E158) No. 64 - Chassis ground: (E158) No. 65 - Chassis ground:	Is the resistance less than 5 Ω?	Go to step 3 .	Open circuit of harness between ECM connector and engine ground terminal
3 CHECK INPUT VOLTAGE OF ECM . Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B134) No. 2 (+) - Chassis ground (-): (B134) No. 27 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 4 .	Repair the open or ground short in the harness of power supply circuit.
4 CHECK M/B (MAIN RELAY) INPUT VOLTAGE . Measure the voltage between M/B (main relay) terminal and chassis ground. Terminals No. 1 (+) - Chassis ground (-): No. 2 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 5 .	Repair the open or ground short in the harness of power supply circuit.
5 CHECK INPUT VOLTAGE OF ECM . Turn the ignition switch to OFF. Install the M/B (main relay). Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B134) No. 60 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Go to step 6 .	Repair the open circuit of harness between ECM connector and M/B (main relay) terminal.
6 CHECK INPUT VOLTAGE OF ECM . Turn the ignition switch to OFF. Connect the connector to ECM. Turn the ignition switch to ON. Measure the voltage between ECM connector and chassis ground. Connector & terminal (B134) No. 1 (+) - Chassis ground (-): (B134) No. 14 (+) - Chassis ground (-):	Is the voltage 10 V or more?	Check ignition control system. <Ref. to IGNITION CONTROL SYSTEM , Diagnostics for Engine Starting Failure.>	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit of harness between ECM connector and M/B (main relay) connector Poor contact of M/B (main relay) connector Poor contact of ECM connector